Explantion of transmission/overdrive behavior?

[SiRaDuDe]

I understand the general workings but we are asking more specific questions here. like:

On 94 + tranny

1. Will it lock-up with OD OFF / 3rd, gear selector on "D"? (we have assumed yes, from quoted posts)

2. Will it lock up at all, with OD off. (again asumed yes, only on "D")

3. WIll it lock up with ECT ON? (from write-up we have a yes on that, just at diferent config)

4. will it lock up on 3rd with OD ON while on "D". (not sure here will assume yes.


While the write-up from the FSM was great!
Its still leaves out a lot of specifis, like at what points lockup accurs, it just states at a certain programed instance but does not go into detail.

"The TCM has programmed in its memory a lock−up clutch operation pattern for each drivingmode (Normal or Power). Based on this lock−up pattern, the TCM turns lock−up solenoid valve on or off in accordance with the vehicle speed signals received from the vehicle speed sensor and the throttle opening signals from the throttle position sensor."


This is vary vauge and details is what we are trying to find out.

While the FSM goes into very detail of when the LOCK disengages it does not go into the same detail of when it engages. Going just by the blue quoted above it would seem the TC lock would not care about OD mode, But it would care about ECT mode. According to same blue quote TC lockup would only care/monitor ECT, Speed Sensor and TP sensor... When I know for a fact the turning off OD will lock up the TC under load. So its gots to be monitoring the OD state also... I assume.... on a A442F

 

[rove_mcanus]

I understand the general workings but we are asking more specific questions here. like:

On 94 + tranny

1. Will it lock-up with OD OFF / 3rd, gear selector on "D"? (we have assumed yes, from quoted posts)

2. Will it lock up at all, with OD off. (again asumed yes, only on "D")

3. WIll it lock up with ECT ON? (from write-up we have a yes on that, just at diferent config)

4. will it lock up on 3rd with OD ON while on "D". (not sure here will assume yes.

1: yes
2: yes electronic models will lock in 3rd or 4th. the a440 behind the 3f only locks in 4th.
3: yes, ect makes it lock at a higher speed.
4: no. If you are in 3rd gear with the OD button on then it's because you are fairly heavy on the throttle, and the lockup will not happen. It will shift into 4th unlocked as you back off and finally into 4th locked.

 

[sleeoffroad]

Christo,

To what tranny does that wripe up apply to?

I will assume to the a442f and the a343f?

Or to just one in specific?

that is out of the 94 repair manual, but I am sure it is pretty similar in later models.

 

[DeeDogga86]

Hi there and sorry for bringing such an old thread back to life but I am too trying to figure out my A442F trans on my 95 24V.
Everything above makes great sense but the only thing which isn't quite clear to me is why the trans shifts down from 4th gear locked to 3rd gear when turning OD off.
Why would it not just jump back into 4th unlocked and then downshift to 3rd depending on the reading of the TPS?
I've been playing around with it a lot but it seems like 4th gear doesn't exist as it immediately shifts into OD even when on slight accel on the highway.

 

[LandLocked93]

Hi there and sorry for bringing such an old thread back to life but I am too trying to figure out my A442F trans on my 95 24V.
Everything above makes great sense but the only thing which isn't quite clear to me is why the trans shifts down from 4th gear locked to 3rd gear when turning OD off.
Why would it not just jump back into 4th unlocked and then downshift to 3rd depending on the reading of the TPS?
I've been playing around with it a lot but it seems like 4th gear doesn't exist as it immediately shifts into OD even when on slight accel on the highway.

Thread context notwithstanding...
"4th" gear IS overdrive.
Turning OFF OD removes "4th" gear from the available gears, so the tranny shifts to its highest gear - 3rd gear.
When you accel at speed, the shift you describe is the tranny shifting out of "4th" gear (OD) into 3rd gear, to accel.

 

[DeeDogga86]

Thanks @LandLocked93.

the bit that was unclear to me was that OD off would take 4th gear out of the selection, I just took it for for what it said and thought it would only avoid from shifting into OD.

Thing is my 80 will flick into 4th gear OD bang on 80kmh... it doesn't seem to be related to "line pressure" at all ... which is all good on flat road as the truck pulls really well when in OD ... which makes me also consider the general performance of my gearbox, it almost feels like a CVT box as it just holds the revs steady while the vehicle accelerates but it's a lot slower in acceleration in 3rd compared to 4th OD.

Thread context notwithstanding...
"4th" gear IS overdrive.
Turning OFF OD removes "4th" gear from the available gears, so the tranny shifts to its highest gear - 3rd gear.
When you accel at speed, the shift you describe is the tranny shifting out of "4th" gear (OD) into 3rd gear, to accel.

 

[LandLocked93]

Thing is my 80 will flick into 4th gear OD bang on 80kmh... it doesn't seem to be related to "line pressure" at all ... which is all good on flat road as the truck pulls really well when in OD

Right. Which sounds like your tranny is in great shape.
The button - apart from it's intent to simply 'turn on or off OD' - is an 'electro-mechanical throttle control' of sorts.
Leaving the button depressed simply allows the tranny to work it out based on your throttle input (only) in any given scenario.
It's a good thing and could be likened to a rudimentary "tow/haul mode" seen more frequently today.